A. Technical Field
The present invention relates to a copolymer for cement admixtures, a cement admixture utilizing the copolymer, and a cement composition, and further, a production process for the copolymer.
B. Background Art
In the recent concrete industry, the improvement of durability and strength of concrete structures is strongly desired, and to reduce the amount of unit water is an important object. Especially, as to polycarboxylic acid-based cement dispersants, many proposals were made, because the polycarboxylic acid-based cement dispersants exhibit higher water reducibility than conventional cement dispersants such as naphthalene-based ones. For example, JP-B-04-68323 proposes polymers as formed from unsaturated carboxylic acid monomer (a) and unsaturated alcohol monomer (b) with a specific combining ratio. However, it is insufficient in capacities as cement dispersants. On the other hand, JP-A-10-236858 proposes a cement dispersant including a copolymer as formed from unsaturated polyalkylene glycol ether monomer (I) and maleic acid monomer (II) with a specific combining ratio. However, much amount of the dispersant is necessary to obtain a sufficient dispersibility because of copolymerizability of monomer (I) and monomer (II), and the dispersant having a level that cannot satisfy the dispersibility particularly in a high water reducing ratio area in the existing circumstances.
A. Object of the Invention
Therefore, an object of the present invention is to provide: a copolymer for cement admixtures which displays high dispersibility with a small adding amount and excellent dispersibility particularly even in a high water reducing ratio area, a production process therefor, a cement admixture utilizing the copolymer, and a cement composition.
B. Disclosure of the Invention
The present inventors diligently studied and, as a result, found that a copolymer, as obtained by using a specific unsaturated polyalkylene glycol ether monomer having a limited polyalkylene glycol chain length and an unsaturated monocarboxylic acid monomer, and polymerizing these monomers under a specific condition, displays high dispersibility with a small adding amount. In addition, they found that: there is a correlation between a state of the motion of the copolymer molecule and a capacity as a cement admixture, and high dispersibility is displayed if a spin-spin relaxation time (T2) of specific signals with 1H-NMR is in a constant range. Then, they completed the present invention on the basis of these findings.
That is to say, copolymer (A) for cement admixtures, according to the present invention, comprises constitutional unit (I) derived from unsaturated polyalkylene glycol ether monomer (a) and constitutional unit (II) derived from unsaturated monocarboxylic acid monomer (b) as essential constitutional units, with the copolymer being characterized in that: unsaturated polyalkylene glycol ether monomer (a) has an alkenyl group having 5 carbon atoms and an oxyalkylene group having 2 to 18 carbon atoms with an average addition number of moles of the oxyalkylene groups to be in the range of 10 to 300.
In addition, copolymer (Axe2x80x2) for cement admixtures, according to the present invention, has: a weight-average molecular weight of not less than 10,000; respective signals detected at the chemical shifts of 0.6 to 1.0 ppm, 1.2 to 1.8 ppm, 1.8 to 2.4 ppm and 3.2 to 3.8 ppm with 1H-NMR; respective signals detected at the chemical shifts of 20.0 to 30.0 ppm, 30.0 to 50.0 ppm, 58.0 to 62.0 ppm and 60.0 to 80.0 ppm with 13C-NMR; and a spin-spin relaxation time (T2) of 1 msec to 50 msec as to the signal observed at 1.2 to 1.8 ppm with 1H-NMR and/or a spin-spin relaxation time (T2) of 1 msec to 90 msec as to the signal observed at 1.8 to 2.4 ppm with 1H-NMR, and unsaturated polyalkylene glycol ether monomer (a) having an alkenyl group having 5 carbon atoms coexists.
A cement admixture, according to the present invention, includes the copolymer for cement admixtures according to the present invention, as an essential component, and may further include a defoaming agent.
A cement composition, according to the present invention, includes the copolymer for cement admixtures according to the present invention, and cement as essential components.
A production process for a copolymer for cement admixtures, according to the present invention, comprises copolymerizing comonomers including unsaturated polyalkylene glycol ether monomer (a) and unsaturated monocarboxylic acid monomer (b) as essential components, with the process being characterized in that: unsaturated polyalkylene glycol ether monomer (a) as used is a compound having an alkenyl group having 5 carbon atoms and an oxyalkylene group having 2 to 18 carbon atoms with an average addition number of moles of the oxyalkylene groups to be in the range of 10 to 300; and a chain-transfer agent is used when copolymerizing the comonomers and/or pH of a resultant reaction mixture after copolymerizing the comonomers is adjusted to not less than 5.
These and other objects and the advantages of the present invention will be more fully apparent from the following detailed disclosure.